JP3295907B2 - Head off-track write prevention method and storage device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a head off-track write prevention method for prohibiting writing to an off-track position where the head position deviates from the correct track, a storage device using the same, and a storage device using the same. The present invention relates to a position prediction method and apparatus used for the method.

[0002]

2. Description of the Related Art For example, in a magnetic disk drive, in order to write data to be recorded on a correct track on a disk, there is a means for prohibiting writing to an off-track position where the head position is off the correct track. Has been adopted. In order to prevent this off-track write, servo servos formed on the disc at regular intervals in advance
A method using a PES (position error signal) obtained from a burst signal obtained by reading a pattern has been conventionally known. JP-A-6-243617 discloses an example of a method using PES.

Recently, in order to prevent the off-track write, a value (P + V) obtained by adding the PES (P) and the speed (V) is used as the next expected PES, and the expected PES is used as a reference. There is also known a method of permitting / prohibiting a write operation by comparing values. In this method, PES (Pn) and speed (V
n = Pn−Pn-1) and the following expected PESn + 1 is calculated based on the obtained Pn and Vn.The expected PESn + 1 = Pn + Vn The absolute values of the calculated Pn, Vn, and PESn + 1 are as follows: | Pn |> C1 | Vn |> C2 | Expected PESn + 1 |> C3 where C1, C2, C3: n-th servo pattern by the constant head and Writing data to the track between the (n + 1) th servo pattern is prohibited.

[0004]

However, in the above-described method using the predicted PESn + 1, the predicted PESn + 1 is considerably different from the actual PESn + 1, and there is a problem that unnecessary write inhibition is performed. That is, as shown in FIG. 4B, the predicted PESn + 1 in the state shown in FIG.
In the first servo pattern, if the actual PESn + 1 exists outside the range of the inhibit criteria with respect to the target track T and does not need to be prohibited from being written, the expected PESn + 1 is inhibit
Unnecessary write prohibition was performed on the track between the n-th servo pattern and the (n + 1) -th servo pattern within the range of the criterion, resulting in an overkill state.

[0005] This is because the predicted PESn + 1 (Pn + Vn) represents the position when the output DAC of the servo controller is in neutral, whereas the servo is always applied.
This is probably because the servo controller's output DAC never goes into neutral. Conventionally, it is also known to calculate an expected PES using a state estimator (Estimator) .However, the state estimator requires a processor such as a high-performance DSP, and is incorporated in a storage device such as a magnetic disk device. Predicting PES would be too expensive, making it impractical for low cost products.

An object of the present invention is to solve the above-mentioned problems,
Head off-track write prevention method capable of reducing overkill due to unnecessary write prohibition when head off-track write is prevented, storage device using the same, and position prediction method and apparatus used therefor It is intended to provide.

Another object of the present invention is to provide a head off-track / write prevention method which enables head off-track / write prevention without requiring a high performance processor such as a DSP. Storage device used, and
An object of the present invention is to provide a position prediction method and apparatus used for the method.

[0008]

According to the present invention, there is provided a head-off device for use in the present invention.
The track write prevention method firstly uses the nth servo
Pn and Vn are obtained from the read values of the pattern, and the output of the servo controller is obtained from Un below. Un = DACn-CENTER_OFF-ki / (1 + k3 + k4) * SPESn where DACn: output of servo controller with bias value added CENTER_OFF bias value at reference position K3, K4, Ki: servo coefficient SPESn: Cumulative value of PES in servo pattern n Next, based on the obtained Pn, Vn and Un, the following expected PE
Find Sn + 1. Expected PESn + 1 = Pn + Vn + kUn Where, Pn: PES (position error signal) in servo pattern n Vn: Speed in servo pattern n (Vn = Pn-Pn-1) Un: Output of servo controller in servo pattern n k: constant Then, when the obtained absolute values of Pn, Vn, and expected PESn + 1 satisfy any of the following conditions, | Pn |> C1 | Vn |> C2 | expected PESn + 1 |> C3 Here, C1, C2, C3: constants Writing of data to the track between the nth servo pattern and the (n + 1) th servo pattern by the head is prohibited.

In a recording apparatus using the off-track write prevention method of the present invention, first, a servo controller provided in a hard disk controller (HDC) comprises n
Pn and Vn from the read value of the servo pattern
And the output of the servo controller is obtained from Un below. Un = DACn-CENTER_OFF-ki / (1 + k3 + k4) * SPESn where DACn: output of servo controller with bias value added CENTER_OFF bias value at reference position K3, K4, Ki: servo coefficient SPESn: Cumulative value of PES in servo pattern n Next, based on the obtained Pn, Vn and Un, the following expected PE
Find Sn + 1. Expected PESn + 1 = Pn + Vn + kUn Where, Pn: PES (position error signal) in servo pattern n Vn: Speed in servo pattern n (Vn = Pn-Pn-1) Un: Output of servo controller in servo pattern n k: constant Then, when the obtained absolute values of Pn, Vn, and expected PESn + 1 satisfy any of the following conditions, | Pn |> C1 | Vn |> C2 | expected PESn + 1 |> C3 Here, C1, C2, C3: constants Writing of data to the track between the nth servo pattern and the (n + 1) th servo pattern by the head is prohibited. There are means for performing the above operations.

In the present invention, in order to obtain an expected PESn + 1,
By considering the output (current) Un of the servo controller, the error between the predicted value of PESn + 1 and the actual value of PESn + 1 can be reduced, and overkill can be reduced. The calculation of the expected PESn + 1 in the present invention is based on the current HDC.
It can be realized by adding a few functions to the servo controller.

The present invention is also directed to a head off-track write prevention method and a position prediction method and apparatus used in a storage device using the same. In this position prediction method and apparatus, position information at the first position is calculated, speed information at the first position is calculated,
Acceleration information at a first position is calculated from the position information and the speed information, and a position at a second position after the first position is calculated from the position information, the speed information, and the acceleration information.

[0012]

FIG. 1 is a diagram showing the configuration of an example of an apparatus for implementing a head off-track write prevention method according to the present invention. In the example shown in FIG. 1, 1 is a magnetic head, 2 is a magnetic disk, 3 is an actuator, 4 is a voice coil motor (VCM), 5 is a hard disk controller (HDC), 6 is a servo controller, 7 Is a track / write prohibition determination unit, 8 is a write prohibition flag, 9 is a D / A converter, and 10 is a VCM driver. In the example shown in FIG. 1, the PES is obtained by reading the servo pattern on the magnetic disk 2 by the magnetic head 1, and the obtained PES and information on the target track are supplied to the servo controller 6. The servo controller 6 calculates an output Un for controlling the VCM 4 based on the supplied PES and information on the target track, and outputs Un. The output Un is supplied to the VCM 4 via the D / A converter 9 and the VCM driver 10. The control of the VCM 4 is performed based on the supplied Un.

A feature of the present invention is that the track / write prohibition determination section 7 makes the following determination. First, Pn and Vn are obtained from the value obtained by reading the n-th servo pattern, and the obtained Pn and Vn and the servo
Based on Un obtained from the output of the controller, the following expected PESn + 1 is obtained. Expected PESn + 1 = Pn + Vn + kUn where Pn: PES (position in servo pattern n
error signal) Vn: Speed in servo pattern n (Vn = Pn-Pn-1) Un: Servo controller output in servo pattern n k: Constant

When the absolute values of the obtained Pn, Vn, and expected PESn + 1 satisfy any of the following conditions, | Pn |> C1 | Vn |> C2 | expected PESn + 1 |> C3 Here, C1, C2, C3: constant It is determined that track / write is prohibited by the head. When the track / write prohibition determination unit 7 determines that the track / write is prohibited, the write prohibition flag 8 of the HDC 4
Is turned ON to prohibit data writing to the track between the nth servo pattern and the (n + 1) th servo pattern.

FIG. 2 is a flow chart for explaining an example when the head off-track write prevention method of the present invention is actually performed by the track / write prohibition judging section 7. Here, as in the above-described example, it is assumed that the n-th servo pattern is read and the expected PESn + 1 is obtained. According to FIG. 2, first, calculate PES and
Pn and Vn are obtained (S1). Next, a determination is made as to whether write is prohibited or write is permitted for each of the obtained Pn and Vn (S2).
If the determination is write prohibition, the write prohibition flag 8 of the HDC 4 is turned on (S3). If the judgment is write permission, the output Un of the servo controller 6 is calculated (S
4). Next, a predicted PESn + 1 (| Pn + Vn + k * Un |) is calculated based on the obtained Pn and Vn and the calculated output Un (S
5). Then, it is determined whether the write is prohibited or the write is permitted based on the calculated expected PESn + 1 (S6). If the determination is write prohibition, the write prohibition flag 8 of the HDC 4 is turned on (S
7). If the determination is write permission, the write prohibition flag 8 is turned on in step S3, and
If the write prohibition flag 8 is turned ON, Un is output to the D / A converter 9 (S8).

In the present invention described above, corresponding to the conventional example shown in FIG. 4, the predicted PESn + 1 of the present invention in the state shown in FIG. 3A in FIG. Expected PESn
+1 and the actual PESn + 1 almost coincide with each other, and the predicted PESn + 1 which is within the range of the inhibitor criterion in the conventional example shown in FIG. Th servo pattern and n + 1
Writing to the track between the third servo pattern is not prohibited.

The bias value at that position is added to the direct output DACn of the servo controller 6.
Therefore, in this example, the output Un of the servo controller 6
Un = DACn-CENTER_OFF-ki / (1 + k3 + k4) * SPESn where DACn: Output of servo controller with bias value added CENTER_OFF: Bias at reference position Value k3, k4, ki: Servo coefficient SPESn: It is preferable to use the accumulated value of PES in servo pattern n.

In the above example, the coefficient k, the constants C1, C
2, C3, and servo coefficients k3, k4, and ki are different depending on the characteristic constants of the device, and optimal values are selected according to the configuration of the device. As an example, for example, the following value is used as the coefficient k in the predicted PESn + 1 of the present invention. k = −0.5 * Kdac * (Kt / J) * Ts ＾ 2 where Kdac: current value per bit of DAC Kt: torque multiplier of VCM Ts: sampling time J: inertia of VCM k described above is DAC (D / A converter) This is an approximate value of the moving distance of the head per bit.

For a certain hard disk drive, when the average error with respect to the position after seeking was calculated based on the predicted PESn + 1 in which the value of k was changed, the results shown in Table 1 below could be obtained. In Table 1, when k is 0, the conventional Pn + V
This shows the case of the expected PESn + 1 consisting of n. From the results in Table 1, when the seek operation is performed based on the predicted PESn + 1 of the present invention in which k is 0.5 to 2.5, the conventional predicted value in which k is 0 is obtained.
It can be seen that the average error is small and the overkill is small compared to the case where the seek operation is performed based on PESn + 1.
Also, from the results in Table 1, it is preferable that k is in the range of 0.5 to 2.5, and it is understood that the next position can be predicted best when k is 1.5, which is more preferable.

[0020]

[Table 1]

Further, the off track of the head of the present invention
When the write prevention method is to be implemented in a hard disk device, for example, the means for implementing the above-described off-track write prevention method is preferably integrated with the servo controller of the HDC as hardware, in other words, the LSI of the HDC. It can be implemented simply by incorporating it into Therefore, the accuracy is the state estimator (Estimat
or), which is inferior to strict PES estimation using PES, but can obtain sufficient practical accuracy, while the present invention does not require a high-performance processor (DSP or the like) unlike a state estimator. In this respect, the conventional off-track write prevention method can be easily implemented at low cost in the conventional hard disk drive.

[0022]

As is apparent from the above description, according to the present invention, since the output (current) Un of the servo controller is considered in order to obtain the expected PESn + 1, the expected PESn + 1 is considered.
The error between the value of PESn + 1 and the actual value of PESn + 1 can be reduced,
Overkill can be reduced. The calculation of the expected PESn + 1 in the present invention can be realized by adding a small function to the servo controller of the current HDC.

[Brief description of the drawings]

FIG. 1 is a diagram showing the configuration of an example of an apparatus for implementing a head off-track write prevention method according to the present invention.

FIG. 2 is a flowchart for explaining an example of a head off-track write prevention method according to the present invention.

FIG. 3 is a diagram for explaining expected PESn + 1 by the head off-track write prevention method of the present invention.

FIG. 4 is a diagram for explaining an expected PESn + 1 by a conventional head off-track write prevention method.

[Explanation of symbols]

Reference Signs List 1 magnetic head, 2 magnetic disk, 3 actuator, 4 VCM, 5HDC, 6 servo controller, 7 track write inhibit judging unit, 8 write inhibit flag, 9 D / A converter, 10 VCM driver

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yukio Fukushima 1 Kirihara-cho, Fujisawa-shi, Kanagawa Japan Inside the Fujisawa Office of IBM Japan, Ltd. (72) Tatsuya Sakai 1 Kirihara-cho, Fujisawa-shi, Kanagawa Japan In the Fujisawa office of IBM Corporation (56) References JP-A-6-103592 (JP, A) JP-A-6-89406 (JP, A) JP-A-10-134532 (JP, A) Kaihei 8-106742 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G11B 21/10

Claims (3)

(57) [Claims] 1. Pn and Vn are obtained from a value obtained by reading an n-th servo pattern, and the output of a servo controller is obtained from the following Un. Un = DACn-CENTER_OFF-ki / (1 + k3 + k4 ) * SPESn where, DACn: Output of servo controller with bias value added CENTER_OFF Bias value at reference position K3, K4, Ki: Servo coefficient SPESn: Cumulative value of PES in servo pattern n Based on Un, the following expected PESn + 1 is obtained, and expected PESn + 1 = Pn + Vn + kUn where Pn: PES (position error signal) in servo pattern n Vn: velocity in servo pattern n (Vn = Pn−Pn) -1) Un: Output of servo controller in servo pattern n k: Constant When the obtained absolute values of Pn, Vn, and expected PESn + 1 satisfy any of the following conditions, | Pn | > C1 | Vn |> C2 | Expected PESn + 1 |> C3 where C1 C2, C3: off-track write method for preventing the head, characterized in that prohibiting writing of data into the track between the n-th servo pattern and the (n + 1) th servo pattern by a constant head. 2. A hard disk controller (HD)
The servo controller provided in C) obtains Pn and Vn from the value obtained by reading the n-th servo pattern, obtains the output of the servo controller from Un below, and Un = DACn-CENTER_OFF-ki / ( 1 + k3 + k4) * SPESn where, DACn: Output of servo controller with bias value added CENTER_OFF Bias value at reference position K3, K4, Ki: Servo coefficient SPESn: Cumulative value of PES in servo pattern n Based on Pn, Vn and Un, the following expected PESn + 1 is obtained, and expected PESn + 1 = Pn + Vn + kUn where Pn: PES (position error signal) in servo pattern n Vn: velocity in servo pattern n ( Vn = Pn-Pn-1) Un: Servo controller output in servo pattern n k: Constant When the calculated absolute values of Pn, Vn, and expected PESn + 1 satisfy one of the following conditions In addition, | Pn |> C1 | Vn |> C2 | Here, C1, C2, C3: means for prohibiting data writing to a track between the nth servo pattern and the (n + 1) th servo pattern by a constant head. Storage device. 3. The storage device according to claim 2, wherein the means for prohibiting data writing in the predetermined case is integrated as hardware.